It is known in the art of injection molding to simultaneously or sequentially inject two melt streams of moldable material into a mold cavity using a single hot runner injection molding nozzle, which is commonly referred to as co-injection. A first melt stream of a first moldable material may be provided by an injection molding machine, which may be referred to as a primary injection unit, while a second melt stream of a second moldable material may be provided by an auxiliary injection unit. The first and second melt streams are fed from their respective injection units into respective, separate first and second melt channels or runners of a manifold that are likewise in fluid communication with respective, separate first and second melt channels of the nozzle through which the melt streams are directed to the mold cavity.
During a co-injection molding operation, controlling the flow of each of the first and second melt streams into the mold cavity is crucial in order to produce consistent multi-layer parts. Conventionally, open loop control of the molding process has been provided by which a signal or such may be sent by the primary injection unit to the auxiliary injection unit, the receipt of which triggers commencement of the injection of the second melt stream by the auxiliary injection unit. The trigger signal may be set-up to permit sequential or simultaneous injection of the first and second melt streams by the primary and auxiliary injection units. The drawback of open loop control is that it provides no mechanism by which the actual molding conditions presented by the flow of the first melt stream injected by the primary injection unit may influence the commencement, speed and/or pressure of the flow of the second melt stream injected by the auxiliary injection unit. Without such real time closed loop control of the auxiliary unit injection, co-injected molded parts may be produced that have layers with inconsistent thicknesses and/or improper/undesirable relative positioning.
Multi-material molding is another type of molding operation in which a primary injection unit as well as an auxiliary injection unit are used to supply the material required to make products, such as, toothbrushes that have a handle made of a first harder material and a gripping surface of a second softer material, and automotive lenses that have a first color portion, e.g., a clear material, forming the main portion of the lens that has a void into which a second color portion, e.g., of an amber material, is molded. These types of multi-material molding applications may use a retracting core, called a “core pull” to create a void into which the second material is injected. Other multi-material operations may use a rotary moving platen with multiple molding stations that mold various features onto a single product as each station engages with a stationary half of the mold. In addition, spin stack molding in which a center block of a stack mold “flips” or rotates to engage different faces of the center block with a stationary half of the mold to define different features of the part being molded is another way multi-material overmolding is performed. In each multi-material application, a first melt stream of a first moldable material may be provided by an injection molding machine, while a second melt stream of a second moldable material may be provided by an auxiliary injection unit, such that, similar to the co-injection molding operation described above, controlling the flow of each of the first and second melt streams into the respective mold cavity is crucial in order to produce consistent multi-material or co-injected molded parts.
As such, a need exists in the art for an injection molding system that provides real time communication of a condition of a first melt stream from a primary injection unit to provide synchronized or slaved injection of a second melt stream from an auxiliary injection unit.